U.S. patent number 7,257,418 [Application Number 09/652,862] was granted by the patent office on 2007-08-14 for rapid user acquisition by a ground-based beamformer.
This patent grant is currently assigned to The DIRECTV Group, Inc.. Invention is credited to Alan Cha, Donald C. D. Chang, Ying Feria.
United States Patent |
7,257,418 |
Chang , et al. |
August 14, 2007 |
Rapid user acquisition by a ground-based beamformer
Abstract
A method for rapid acquisition of a specific subscriber by a
ground-based beamformer includes the steps of defining a coverage
area as an arrangement of a plurality of cells wherein one of the
plurality of cells includes a specific subscriber; defining a
partition of cell clusters wherein one of the cell clusters
includes the one of the plurality of cells that includes the
specific subscriber; forming a beam that corresponds to an area of
one of the cell clusters; and scanning the beam to the cell cluster
that includes the specific subscriber.
Inventors: |
Chang; Donald C. D. (Thousand
Oaks, CA), Cha; Alan (Glendale, CA), Feria; Ying
(Manhattan Beach, CA) |
Assignee: |
The DIRECTV Group, Inc. (El
Segundo, CA)
|
Family
ID: |
38337098 |
Appl.
No.: |
09/652,862 |
Filed: |
August 31, 2000 |
Current U.S.
Class: |
455/458;
455/12.1; 455/427 |
Current CPC
Class: |
H04B
7/18545 (20130101); H04B 7/18504 (20130101); H04W
84/06 (20130101) |
Current International
Class: |
H04Q
7/20 (20060101) |
Field of
Search: |
;455/12.1,13.1,427,429,456,562,458 ;342/357.01,357.16,457
;244/158R |
References Cited
[Referenced By]
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|
Primary Examiner: Trost; William
Assistant Examiner: Ewart; James D
Attorney, Agent or Firm: Grunebach; Georgann S.
Claims
The invention claimed is:
1. A method for rapid acquisition of a specific subscriber
comprising the following steps: (a) defining a coverage area as an
arrangement of a plurality of cells wherein one of the plurality of
cells includes a specific subscriber; (b) defining a partition of
cell clusters wherein one of the cell clusters includes the one of
the plurality of cells that includes the specific subscriber; (c)
forming a beam that corresponds to an area of one of the cell
clusters; and (d) sequentially scanning the beam to each of the
cell clusters until the one of the cell clusters that includes the
specific subscriber is identified.
2. The method of claim 1 wherein step (b) includes defining the
partition from a traffic model to enhance acquisition of the
specific subscriber.
3. The method of claim 1 further comprising after step (d) the step
of (e) partitioning the cell cluster that includes the specific
subscriber into a plurality of cell clusters.
4. The method of claim 3 wherein each of the plurality of cell
clusters has an equal number of cells.
5. The method of claim 3 further comprising after step (e) the step
of (f) zooming the beam to form a beam that corresponds to an area
of one of the plurality of cell clusters.
6. The method of claim 5 wherein step (f) comprises combining beams
corresponding to an area of at least one of the plurality of cells
to form the beam.
7. The method of claim 5 further comprising the step of repeating
steps (d), (e), and (f).
8. An apparatus for rapid acquisition of a specific subscriber
comprising: a stratospheric transponder platform having an antenna
for one of transmitting and receiving a beam; and a ground station
coupled to the stratospheric transponder platform wherein the
ground station comprises a beamformer for zooming a beam
corresponding to an area of a cell cluster within a partition
containing a plurality of cell clusters and sequentially scanning
the beam to aim at each of the cell clusters until one of the
plurality of cell clusters that includes the specific subscriber is
identified.
9. The apparatus of claim 8 wherein the ground station further
comprises a traffic model module for defining the partition.
10. The apparatus of claim 8 wherein each of the plurality of cell
clusters has an equal number of cells.
11. The apparatus of claim 8 wherein the beamformer zooms the beam
by combining beams corresponding to an area of at least one of the
plurality of cells.
12. A method for rapid acquisition of a specific subscriber
comprising the following steps: (a) defining a coverage area as an
arrangement of a plurality of cells wherein one of the plurality of
cells is a specific subscriber cell including the specific
subscriber; (b) partitioning the plurality of cells into cell
clusters each formed from more than one of the plurality of cells
wherein one of the cell clusters includes the specific subscriber
cell; (c) forming a beam that corresponds to an area of one of the
cell clusters; (d) sequentially scanning the beam to each of the
cell clusters until the one of the cell clusters that includes the
specific subscriber is identified; (e) partitioning the one of the
cell clusters that includes the specific subscriber into a second
plurality of cell clusters; (f) zooming the beam to form a beam
that corresponds to an area of one of the second plurality of cell
clusters; and (g) sequentially scanning the beam to each of the
second plurality of cell clusters until one of the second plurality
of cell clusters that includes the specific subscriber is
identified; and (h) determining a location of the specific
subscriber cell in response to scanning the beam to one of the
second plurality of cell clusters that includes the specific
subscriber.
13. The method of claim 12 wherein partitioning the plurality of
cells comprises partitioning the plurality of cells in response to
a traffic model.
14. The method of claim 12 wherein partitioning the plurality of
cells into cell clusters comprises partitioning the plurality of
cells into clusters each having an equal number of cells.
15. A method for rapid acquisition of a specific subscriber
comprising: defining a coverage area having a plurality of cells
wherein one of the plurality of cells includes the specific
subscriber generating a locating signal; defining at least a first
cell cluster and second cell cluster within the plurality of cells;
zooming a beam to a first size; sequentially scanning the first
cell cluster and the second cell cluster; identifying the first
cell cluster when the locating signal is received therefrom;
partitioning the first cell cluster into a third cell cluster and a
fourth cell cluster; zooming the beam to a second size; thereafter,
confirming the specific subscriber is within the third cell cluster
in response to the locating signal; and partitioning and zooming
until a location of the specific subscriber is determined.
16. The method of claim 15 wherein zooming a beam to a first size
comprises zooming a beam to a first size corresponding to an area
of the first cell cluster or the second cell cluster.
17. The method of claim 15 wherein zooming the beam to a second
size comprises zooming a beam to a second size corresponding to an
area of the third cell cluster or the fourth cell cluster.
18. The method of claim 15 wherein partitioning the plurality of
cells comprises partitioning the plurality of cells into an equal
number.
19. A method for rapid acquisition of a specific subscriber
comprising: defining a coverage area having a plurality of cells
wherein one of the plurality of cells includes a specific
subscriber cell having a specific subscriber therein; and
partitioning the cells into progressively smaller clusters; and
zooming and sequentially scanning a beam to the progressively
smaller clusters until a location of said specific subscriber cell
is determined.
20. A method for rapid acquisition of a specific subscriber
comprising: defining a coverage area having a plurality of cells
wherein one of the plurality of cells includes a specific
subscriber generating a locating signal; defining a first cell
cluster from the plurality of cells according to a traffic model;
zooming and sequentially scanning a beam to a first size
corresponding to the first cell cluster; confirming that the
specific subscriber is within the first cell cluster; partitioning
the first cell cluster into a second cell cluster and a third cell
cluster; zooming and sequentially scanning the beam to a second
size; thereafter, confirming that the specific subscriber is within
the third cell cluster; and partitioning and zooming until a
location of the specific subscriber cell is determined.
21. The method of claim 20 wherein confirming that the specific
subscriber is within the first cell cluster comprises receiving the
locating signal from the user.
22. The method of claim 20 wherein zooming the beam to a second
size comprises zooming the beam to a second size corresponding to
the third cell cluster.
23. A method for rapid acquisition of a specific subscriber
comprising: defining a coverage area having a plurality of cells
wherein one of the plurality of cells includes a specific
subscriber having a first acquisition code address and a second
acquisition code address associated therewith; performing a first
acquisition method and a second acquisition method in parallel
until a location of a specific subscriber cell is determined,
wherein performing a first acquisition method comprises using a
first acquisition code address, partitioning the cells into first
progressively smaller clusters; and zooming and scanning a first
beam to the first progressively smaller clusters; and performing a
second acquisition method comprises using a second acquisition code
address, partitioning the cells into second progressively smaller
clusters according to a traffic model; and zooming and scanning a
second beam to the second progressively smaller clusters.
Description
BACKGROUND OF THE INVENTION
The present invention relates generally to ground-based
beamformers. More specifically, but without limitation thereto, the
present invention relates to finding a cell in which a specific
user is located within the coverage area of a stratospheric
transponder platform linked to a ground-based beamformer.
An antenna array on a stratospheric transponder platform can
support multiple subscribers dispersed over a wide coverage area.
To reduce weight, power consumption, and cost of the stratospheric
transponder platform, a ground-based digital beamformer may be used
that performs the beam calculations on the ground from a ground
station linked to the antenna elements on the stratospheric
transponder platform. In this arrangement, the element excitation
signals are passed between the antenna elements on the
stratospheric transponder platform and the digital beamformer in
the ground station using CDMA techniques, for example.
Solar powered stratospheric transponder platforms have the
capability of staying aloft for a long period of time, but their
weight and power generation capacity are disadvantageously limited.
Ground-based digital beamforming removes the weight and power
requirements of the beamformer from the stratospheric platform to
the ground station, and also provides an advantageous system
architecture known as "spokes and hub." In this architecture, all
system data and communications processing functions are co-located
in the ground station. Because system data does not have to be
passed back and forth between the stratospheric transponder
platforms and the ground station, valuable communications resources
are conserved, resulting in faster processing time and system
response.
An important function performed by communications systems including
ground stations in a spokes and hub architecture is acquiring a
specific subscriber, i.e., locating the cell in a platform coverage
area in which a specific subscriber is located.
FIG. 1 is a diagram illustrating a method 100 for locating a
specific subscriber 102 in a coverage area 104. According to the
method 100, each cell 106 within the coverage area 104 is scanned
by stepping a beam 108 from a beamformer located in a stratospheric
transponder platform 120 sequentially to each cell 106 until the
cell containing the specific subscriber 102 is located. Although a
communications satellite is used to illustrate a transponder
platform in this example, other transponder platforms may be used,
such as unmanned aircraft and antenna towers
In this example, the coverage area 104 is 64 km.times.64 km and is
divided into 64 cells 106 that are each 8 km.times.8 km. The beam
108 is stepped in raster scan fashion from cell to cell in each
row, and from one row to the next until the specific subscriber 102
is located, in this example, after stepping the beam 108 30 times.
Assuming a dwell time of T, locating the specific subscriber 102
requires from T to 64 T, depending on where the cell containing the
specific subscriber 102 is located.
Disadvantageously, the method 100 requires an average acquisition
time of 32T, or more generally, NT/2, where N is the number of
cells in the coverage area. Because N may be a large number,
processing the many beams slows acquisition time and thus adversely
affects the system response.
SUMMARY OF THE INVENTION
The present invention advantageously addresses the needs above as
well as other needs by providing a method and apparatus for rapid
acquisition of a specific subscriber within a coverage area of a
transponder platform.
In one embodiment, the invention may be characterized as a method
for rapid acquisition of a specific subscriber that includes the
steps of defining a coverage area as an arrangement of a plurality
of cells wherein one of the plurality of cells includes a specific
subscriber; defining a partition of cell clusters wherein one of
the cell clusters includes the one of the plurality of cells that
includes the specific subscriber; forming a beam to correspond to
an area of one of the cell clusters; and scanning the beam to the
cell cluster that includes the specific subscriber.
In another embodiment, the invention may be characterized as a
ground-based beamformer for rapid acquisition of a specific
subscriber that includes a stratospheric transponder platform
having an antenna for one of transmitting and receiving a beam; and
a ground station coupled to the stratospheric transponder platform
wherein the ground station comprises a beamformer for at least one
of zooming the beam to form a beam corresponding to an area of a
cell cluster within a partition containing a plurality of cell
clusters and scanning the beam to one of the plurality of cell
clusters that includes a specific subscriber.
The features and advantages summarized above in addition to other
aspects of the present invention will become more apparent from the
description, presented in conjunction with the following
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
The above and other aspects, features and advantages of the present
invention will be more apparent from the following more specific
description thereof, presented in conjunction with the following
drawings wherein:
FIG. 1 is a diagram illustrating a method for locating a specific
subscriber in a coverage area;
FIG. 2 is a diagram illustrating a method for locating a specific
subscriber in a coverage area by zooming and scanning according to
an embodiment of the present invention;
FIGS. 3A 3C are beam plots illustrating an exemplary method for
zooming a beam that may be used with the method illustrated in FIG.
2;
FIG. 4 is a diagram illustrating the method illustrated in FIG. 2
further enhanced by including a traffic model;
FIG. 5 is a block diagram of an exemplary ground-based beamformer
that may be used to implement the methods illustrated in FIGS. 2
and 4; and
FIG. 6 is a flow chart of the method of FIG. 2 for rapid user
acquisition for stratospheric transponder platforms by a
ground-based beamformer.
Corresponding reference characters indicate corresponding elements
throughout the several views of the drawings.
DETAILED DESCRIPTION OF THE DRAWINGS
The following description is presented to disclose the currently
known best mode for making and using the present invention. The
scope of the invention is defined by the claims.
The method 100 illustrated in FIG. 1 described above for locating
the specific subscriber 102 in the coverage area 104 may be
implemented by a ground-based beamformer in a CDMA communications
system gateway hub 122. By locating the beamformer at the ground
station, the disadvantages of the added weight and power required
to include a beamformer in the payload of a stratospheric
transponder platform 120 may be advantageously avoided. Also, the
separate beam signals and control signals do not have to be passed
back and forth between the ground station and the transponder
platform, thus reducing the communications traffic overhead of the
system. An example of a ground-based digital beamformer will be
described later with reference to FIG. 5.
FIG. 2 is a diagram illustrating another method 200 for locating a
specific subscriber in a coverage area by performing both zooming
and scanning of a beam. The beam may be formed by a beamformer on
the transponder platform or by a ground-based beamformer using the
CDMA communications system in the example of FIG. 1. The coverage
area 104 is defined by the arrangement of a plurality of cells 106.
In this example, each of the cells 106 has the same area. An
initial 8.times.8 cell cluster 201 is defined that, in this
example, includes the entire coverage area. A beam 202 is zoomed to
form a beam that corresponds to the area of the initial cell
cluster 201. A locating signal is received from the specific
subscriber 102 that confirms that the specific subscriber 102 is in
one of the cells 106 included in the initial cell cluster 201. The
initial cell cluster 201 is then partitioned into four new
4.times.4 cell clusters 204, 206, 208, and 210. The beam 202 is
zoomed to become the smaller beam 212 that corresponds to the area
of one of the new 4.times.4 cell clusters 204, 206, 208, and 210
and is scanned or stepped in raster fashion to each new cell
cluster successively until a locating signal is received from the
specific subscriber 102. The cell cluster containing the specific
subscriber 102, i.e., cell cluster 208, is then partitioned into
four new 2.times.2 cell clusters 224, 226, 228, and 230. The beam
212 is zoomed to become the smaller beam 214 that corresponds to
the area of one of the new 2.times.2 cell clusters 224, 226, 228,
and 230 and is scanned in raster fashion to each new cell cluster
successively until a locating signal is received from the specific
subscriber 102 in cell cluster 230. The cell cluster 230 containing
subscriber 102 is then partitioned into four new 1.times.1 cell
clusters 234, 236, 238, and 240. The beam 214 is zoomed to become
the smaller beam 216 that corresponds to the area of one of the new
1.times.1 cell clusters 234, 236, 238, and 240 and is scanned in
raster fashion to each new cell cluster until a locating signal is
received from subscriber 102 in cell cluster 240. Because the new
1.times.1 cell clusters 234, 236, 238, and 240 now contain only one
cell each, the specific subscriber 102 has now been located or
acquired.
Only 10 beam steps were required in this example compared to 30
steps in the example of FIG. 1, thus reducing the total dwell time
by 67 percent. On average, a dwell time of only 8.5T (based on a
minimum of four and a maximum of 13 beam steps) is required for the
approach used in this example compared to 32T in the approach of
FIG. 1, nearly four times faster.
Another advantage of the method 200 of FIG. 2 is that it may be
implemented with existing ground-based digital beamformers simply
by adding software using standard beamforming functions and a beam
zooming method, such as the one described below. As an example, the
ground-based beamformer in a CDMA communications system gateway hub
122 in FIG. 1 can perform the zooming and scanning of the beam
214.
FIGS. 3A 3C are beam plots illustrating a method 300 for zooming a
beam that may be used with the embodiment illustrated in FIG. 2. In
FIG. 3A, individual beams 302, 304, 306, and 308 each have a width
angle .theta. that corresponds to the area of one of the plurality
of cells 106 in FIG. 2. In FIG. 3B, the beams 302 and 304 are added
to form a zoomed beam 310, and the beams 306 and 308 are added to
form a zoomed beam 312. Each of the zoomed beams 310 and 312 has
twice the width angle of the individual beam 302, thus
corresponding to a cell cluster size of 2.times.2, or four
cells.
In FIG. 3C, the zoomed beams 310 and 312 are added to form a zoomed
beam 320 that has four times the width angle of the individual beam
302, thus corresponding to a cell cluster size 4.times.4, or 16
cells. Other beam combinations may be used according to this method
to zoom beams to correspond to the areas of various cell cluster
sizes.
FIG. 4 is a diagram illustrating the method illustrated in FIG. 2
further enhanced by a traffic model. A further advantage of beam
zooming is realized by adapting to a real-time communications
traffic pattern that may have a diurnal cycle and differ from zone
to zone within the coverage area. Traffic models may be updated,
stored, and accessed in the traffic model by a ground-based
beamformer to further reduce the acquisition time. The "spokes and
hub" architecture is well suited to the use of traffic models
because cell size and search strategy based on traffic conditions
and models may be updated at the gateway hub without passing
information back and forth between the gateway hub and the
transponder platform, thus conserving valuable communications
resources.
Special events may have a great influence on the traffic model. For
example, an initial 2.times.2 cell cluster 402 that is smaller than
the coverage area 104 may be defined for a known high traffic area
stored in the traffic model that contains only four 1.times.1 cell
clusters 416, 418, 420, and 422. The beam 202 is zoomed directly to
the beam 414 that corresponds to the area of the cell cluster 402,
and a locating signal is received from the specific subscriber 102
that confirms that the specific subscriber 102 is in one of the
cells 106 included in the initial cell cluster 402. The initial
cell cluster 402 is partitioned into four new 1.times.1 cell
clusters 416, 418, 420, and 422, and the beam 414 is zoomed to the
beam 415 that corresponds to the area of one of the four new
1.times.1 cell clusters 416, 418, 420, and 422. The beam 415 is
scanned sequentially until the specific subscriber 102 is acquired
in the cell cluster 420.
Based on the traffic model, there is a high probability that the
position of the specific subscriber 102 is in the high traffic area
defined by the cell cluster 402, which is much smaller than the
entire coverage area 104. The reduced initial cluster size
advantageously reduces the size of the initial cell cluster and
consequently the total dwell time even further than the method
illustrated in FIG. 2. Alternatively, a sequential search using
mixed cell cluster sizes may be used if only one acquisition code
address for subscriber 102 (e.g., CDMA systems) is used. If two
acquisition code addresses are used for subscriber 102, the high
traffic area may be allocated a dedicated acquisition code and two
searches may be conducted in parallel using two beams. One beam
would be used to perform the search described with reference to
FIG. 2, and the other beam would be used to perform the search
described with reference to FIG. 4. If the position of subscriber
102 is successfully predicted by the traffic model, the latter
search would be terminated before the former, thus reducing the
acquisition time by the fastest method.
The traffic model allows the acquisition of the specific subscriber
102 to be adapted to real-time traffic conditions stored in user
position files residing in the gateway station or hub 122. In
communications systems having a beamformer in the transponder
platform, the traffic model information would have to be
transmitted back and forth between the gateway and the transponder
platform, which would actually increase the time delay for
acquiring the specific subscriber 102. In a ground based
beamforming system, however, the traffic model may advantageously
be implemented in the ground station without the delay of relaying
the traffic model information to the transponder platform.
FIG. 5 is a block diagram of an exemplary ground-based beamformer
500 that may be used to implement the methods illustrated in FIGS.
2 and 4. The ground-based beamformer 500 includes a ground station
52 and a stratospheric transponder platform 54.
Shown in the ground station 52 are a data processor 506 that
interfaces in this example with communications traffic 504 to and
from internet service providers 502, a traffic model module 508, a
digital beamformer 509, beam signals (1-N) 510, element signals
(1-M) 512, a CDMA multiplexer/demultiplexer 514, CDMA signals 515,
A C- or X-band RF subsystem 516, and a feeder link 518.
The data processor 506 performs multiplexing, demultiplexing,
routing, and formatting of beam signals 510 according to well-known
techniques. The data processor 506 is coupled to the digital
beamformer 509 and includes the functions of beam zooming and
scanning beams in raster sequence as described above and
illustrated in FIG. 2.
The traffic model module 508 coupled to the data processor 506 may
be included for storing and updating traffic models as described
above to further improve subscriber acquisition time as illustrated
in FIG. 4. The traffic model module 508 includes the user position
files and real-time traffic conditions as described for FIG. 4.
The beam signals 510 are received as input to the digital
beamformer 509 when transmitting to the subscribers 534 or
generated as output from the digital beamformer 509 to the data
processor 506 when receiving signals from the subscribers 534. The
digital beamformer 509 receives as inputs or generates as outputs
element signals 512 corresponding to the beam signals 510. The
digital beamformer 509 may be implemented using well-known
techniques. A code division multiple access (CDMA) mux/demux 514
multiplexes/demultiplexes the element signals 512 as described
above to/from a C- or X-band RF subsystem 516 according to
well-known techniques. The C- or X-band RF subsystem 516
inputs/outputs CDMA signals 515 and transmits/receives C- or X-band
signals 517 to/from a feeder link 518 that links the element
signals 512 between the ground station 52 and the stratospheric
transponder platform 54.
The stratospheric transponder platform 54 includes a feeder link
522, a C- or X-band RF subsystem 524, and a CDMA mux/demux 526 that
may be implemented according to well known techniques as described
above. An S-band RF subsystem 530 amplifies element signals (1-M)
528 for transmitting/receiving by an antenna array 532 to/from the
subscribers 534 on the beams 108. The operation of antenna array
532 is assumed to be reversible between transmit and receive modes,
thus the beamforming method of this example applies both to
transmitting and receiving signals. The stratospheric transponder
platform 54 may be, for example, a communications satellite, an
unmanned aircraft, or an antenna tower.
For the user acquisition function, the stratospheric transponder
platform 54 and the gateway hub 52 only receive the locating signal
and do not transmit any signals to the subscriber 534 being
acquired. Thus, in FIG. 5, the locating signal originates from the
subscriber 534 being acquired and is relayed by the stratospheric
transponder platform 54 to the gateway hub 52. When receiving the
locating signal from the subscriber 534 being acquired, the inputs
to the digital beamformer are the element signals 512 and the
outputs are the beams 510. One or two of the beams may be used for
user acquisition. The zooming and scanning functions may be
performed mathematically in the digital beamformer in two steps:
(1) multiplying the M element signals by an appropriate set of M
weights represented as complex numbers, and (2) summing the M
weighted signals to determine the output beam signal. The sets of
complex weights may be computed using well known techniques.
FIG. 6 is a flow chart 600 of the method illustrated in FIG. 2 for
rapid user acquisition for stratospheric transponder platforms by
beams formed by the ground-based beamformer of FIG. 5. Step 602
defines a coverage area as an arrangement of cells such as that
shown in FIG. 2. Step 604 defines an initial cell cluster that
includes the cell containing the specific subscriber. The initial
cluster may be selected as the entire coverage area or a portion of
the coverage area determined by a traffic model as explained above.
Step 606 zooms the beam to form a beam that corresponds to an area
of one of the cell clusters. Step 608 scans the beam to the cell
cluster that includes the specific subscriber. Step 610 partitions
the cell cluster that includes the specific subscriber to define a
new partition of cell clusters. Step 612 repeats steps 606, 608,
and 610 until the partition contains only one cell, i.e., the cell
containing the specific subscriber.
Other modifications, variations, and arrangements of the present
invention may be made in accordance with the above teachings other
than as specifically described to practice the invention within the
spirit and scope defined by the following claims.
* * * * *